A critical part of business operations in the well drilling industry is equipment testing. Part of that equipment includes lengths of pipe which are extended down well holes and remain in place for several years under adverse conditions. Should a pipe segment fail, the costs associated with correcting such a failure are prohibitively high and, in some instances, the failure may even be irreparable. As such, pressure testing pipe segments has become an integral part of preparing and testing the equipment to be used in creating a well.
There have developed two widespread methods of pressure testing pipe segments. The first is known as "rack" testing. This testing method involves threading each end of a pipe segment with a plug and thereafter pumping fluid into the internal cavity of the pipe until a predetermined test pressure has been reached. Upon completion of the test, the pressure is released and the end plugs removed from the pipe segments.
A second method of pipe testing is known as the "mill" testing procedure. The mill tester is a large machine which is capable of simultaneously gripping and plugging off the opposite ends of a pipe segment. This gripping and plugging action takes place in a trough of fluid so that when the pipe segment is initially gripped by the tester, the pipe segment is at least partially filled with fluid. The remaining voids within the pipe are then pumped full with fluid through the mill tester end plugs. The fluid is pressurized to a desired predetermined test pressure, the pressure is then released and the pipe removed from the trough.
There are several drawbacks associated with each of the prior art methods of pipe segment pressure testing. With regard to the "rack" test, the drawbacks are that the pipe end portions are threaded and unthreaded several times over the useful life of a pipe for testing purposes only. As such, the threads can become worn and possibly misaligned during the several threading and unthreading procedures. Further, the mechanisms which are used to thread the segments of pipe with plugs often cause minor damage to the exterior of the pipe owing to their gripping action. The major drawback to this method of testing, however, is related more to the advancements in the material composition of the pipe. Specifically, advances in materials have made pipe segments far more resistant to failures associated with internal pressure. As such, the predetermined test pressures have increased to the extent that the plugs mounted on the respective ends of a pipe segment can no longer withstand the pressure. This is because the area of a plug end which is resisting the pressure is equivalent to the full cross-sectional area of a pipe. If a pipe diameter is 8 inches and the testing pressure 20,000 PSI, the accumulated pressure which the end plug must resist is approximately 500 tons of force.
The advancement in material compositions of the pipe has also created several drawbacks to the mill testing method. Specifically, as the pipe materials have advanced in their strength the associated mill testers have also necessarily advanced in their capacity to exert sufficient pressure on the ends of the pipe segments during testing. As such, the mill testing apparatus has become extremely bulky and virtually immobile. Further, as materials advance even further it is uncertain whether a mill tester can be built which could withstand the necessary end pressures so as to properly test a pipe segment.
Another method of testing pipe segments, disclosed in U.S. Pat. No. 4,557,139, was developed so as to test the threaded joints between adjacent pipe sections. This method was developed primarily to test a length of related pipe segments in a vertical orientation in a derrick. Particularly, a testing apparatus was inserted into the open upper end of a series of pipe segments and lowered therethrough and placed so as to correspond to successive threaded joints of the related pipe segments. The testing tool was sealed at each end thereof to the inner surfaces of the pipe and fluid was pumped into the annular cavity separating the testing tool and the pipe segments. In this manner, several threaded joints could be tested in series without the need for separating the related pipe segments.
From this vertical testing procedure, there was developed a horizontal pipe testing procedure whereby pipe lengths could be laid down onto a substantially horizontal rack and a pipe testing tool would be inserted therein, pressured up, and the pipe segments tested. However, pipe segments come in several different lengths ranging from approximately 20 feet to 60 feet. As a result, the pipe tester was also made to be necessarily capable of being configured in several lengths. The drawback of this testing method was the time consuming assembly and disassembly of the pipe tester into the several lengths required by the varied pipe segment dimensions.